The word thunder has an etymology that's simple, short, and sweet: it's from Old English thunor, from Proto-Germanic thunraz, from Proto-Indo-European tenh. It's the connections we can draw from this that are fascinating. Probably with a jaunt through Proto-Italic, tenh landed itself in Latin in the form tornare, still "to thunder". This developed into the Spanish word tronar, which later became tronada, now with a meaning more like "thunderstorm"; not that far of a stretch. Then, in the mid-sixteenth century, English sailors picked up the term from Spanish sailors, but accidentally combined it with the verb tornar ("to twist"), so that they switched the r and o sounds. This mutt of a combination formed tornado, which is oddly appropriate, considering it is a twisting thunderstorm. An alternative spelling of ternado was also created but never caught on.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.